CN113176079A - Ultrahigh-precision wavefront detection and calibration method for high-contrast imaging coronagraph - Google Patents
Ultrahigh-precision wavefront detection and calibration method for high-contrast imaging coronagraph Download PDFInfo
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- CN113176079A CN113176079A CN202110539542.6A CN202110539542A CN113176079A CN 113176079 A CN113176079 A CN 113176079A CN 202110539542 A CN202110539542 A CN 202110539542A CN 113176079 A CN113176079 A CN 113176079A
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Abstract
The invention discloses an ultrahigh-precision wavefront detection and calibration method for a high-contrast imaging coronagraph, which comprises the following steps of: step 1, building a set of coronagraph system with a deformable mirror as a core; step 2, controlling a coronagraph control system to send a first control signal to a deformable mirror to enable the deformable mirror to generate an ultrahigh contrast dark area on a focal plane, and shooting a focal plane image at the moment as a reference image; step 3, according to the wavefront detection precision design index of the coronagraph, applying a second control signal to the deformable mirror; and 4, judging whether the wavefront detection precision of the system meets the design requirement or not by evaluating the difference between the reference wave surface and the wave surface in the step 3. The method of the invention does not need to introduce additional detection components, only needs to utilize the deformable mirror of the coronagraph and apply control signals to the deformable mirror through the deformable mirror, and can realize ultra-high precision wavefront detection and calibration through evaluating the dark image of the focal plane.
Description
Technical Field
The invention relates to the field of extrasystematic planet ultrahigh contrast imagers, in particular to an ultrahigh precision wavefront detection and calibration method for a high contrast imaging coronagraph.
Background
The solar extrasolar planet detection has great scientific significance for understanding the origin and evolution of life and recognizing the position of human in the universe. The final goal is to search for planets around the earth mass in the solar-like spectral star livable zone and finally solve the "whether humans are solitary in the universe? "this basic scientific problem. However, because the contrast of the radiation of the planet-like planet is very different from that of the main planet and the distance from the main planet is short, the weak photon signals from the planet are submerged in the extremely strong sidereal background.
At present, the extraterrestrial planet direct imaging coronagraph developed at home and abroad can only observe in an infrared wave band, and the imaging contrast can only reach 10-6Magnitude. The corresponding wavefront measurement and calibration accuracy need only be on the order of 1/100 wavelengths. However, because the contrast of the radiation of the geostationary planet is very different from that of the main planet, the imaging contrast is usually 10-6～10-10In the range of (1), the corresponding wave aberration measurement and calibration accuracy is 1/100-1/10000 working wavelength. The conventional technical means such as a shack Hartmann wavefront sensor, a traditional phase interferometer and other measurement technologies at present are difficult to achieve such high wavefront detection and calibration accuracy. Therefore, a simple and effective method for wavefront detection and calibration is an urgent problem to be solved by those skilled in the art.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an ultrahigh-precision wavefront detection and calibration method for a high-contrast imaging coronagraph. According to the method, the deformable mirror in the coronagraph system is controlled to generate a specific control signal, and then the ultrahigh contrast dark area of the focal plane is evaluated to realize ultrahigh-precision wavefront detection and calibration.
The technical scheme of the invention is as follows:
ultrahigh-precision wavefront detection and calibration method for high-contrast imaging coronagraph, aiming at contrast ratio superior to 10-6Above thatThe wavefront detection and calibration precision of the coronagraph is within the range of 1/100-1/10000 working wavelength, and the method comprises the following specific steps:
step 2, the coronagraph control system sends a first control signal to the deformable mirror, a high-contrast dark area is generated on a focal plane, and N focal plane images are shot by using a focal plane camera;
step 3, averaging the N images collected in the step 2 to obtain a reference image, sequentially calculating RMS values of the reference image and the N focal plane images collected in the step 2, and averaging the calculated RMS values to obtain a reference RMS value; step 4, calculating according to the wavefront detection precision of the coronagraph and the effective stroke of the deformable mirror to obtain a second control signal of the deformable mirror, adding the second control signal and the first control signal, sending the second control signal to the deformable mirror through the coronagraph control system, and shooting a focal plane image of the system;
Further, in step 3 and step 4, the following evaluation function is adopted in the evaluation process:
where m and n are the number of rows and columns of the image, xmnIs the pixel value, x 'of the image obtained in the step 3 at the position of (m, n)'mnThe pixel value of the image shot in step 4 or step 1 at the (m, n) point.
Furthermore, the wavefront detection and calibration method only uses a deformable mirror and a focal plane camera in the coronagraph, and does not need additional devices.
Further, the relative wavefront accuracy is detected, i.e. the step 3 generated wavefront changes relative to the step 2 wavefront are detected rather than the absolute wavefront accuracy.
The invention has the beneficial effects that:
according to the detection and calibration method, additional detection components are not required to be introduced, only a deformable mirror in the crown instrument is required to be utilized, a specific control signal is applied to the deformable mirror, and wavefront detection and calibration of the system can be achieved by evaluating the dark image of the focal plane of the system; compared with the traditional wave-front detection technology, the method has higher wave-front detection precision.
Drawings
Figure 1 is a schematic view of a coronagraph optical system;
fig. 2 is a graph of the results of laboratory testing.
Wherein, the system comprises a 1-collimating lens, a 2-swinging mirror, a 3-distorting mirror, a 4-coronagraph and a 5-focal plane camera.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to an ultrahigh-precision wavefront detection and calibration method for an ultrahigh-contrast coronagraph, in particular to a method for detecting and calibrating relative wavefront precision, which is implemented according to the following steps: step 1, building a set of optical system of the coronagraph. Wherein the anamorphic mirror is placed at the pupil of the system and is conjugate to the primary mirror of the telescope.
As shown in FIG. 1, in this embodiment, after being collimated by a collimating mirror 1, the light of the telescope is reflected by a swing mirror 2 and a deformable mirror 3 (the swing mirror is used for image stabilization; the deformable mirror is used for correcting speckle noise in the system), and both the swing mirror and the deformable mirror need to be respectively conjugated with a primary mirror of the telescope; the light from the telescope then enters the coronagraph 4 and is finally imaged in the focal plane camera 5. The coronagraph control system is respectively connected with the swing mirror, the deformable mirror and the focal plane camera. It should be noted that the specific implementation of the optical system of the corollary instrument (including the selection of the optical elements such as the collimating mirror 1 and the tilting mirror 2) for achieving the objectives of the present invention can be determined according to specific needs, and this embodiment is only exemplified as a preferred implementation with reference to the specific structure in fig. 1.
Step 2, the coronagraph control system sends a first control signal to the deformable mirror, a high-contrast dark area is generated on a focal plane, and N images of the dark area are continuously shot through a focal plane camera;
step 3, due to the limitation of camera noise and the repetition precision of the deformable mirror, the focal plane images shot in the step 2 have certain difference, and the dark areas of each image are not completely the same, so that N images collected in the step 2 are required to be averaged to be used as reference images, RMS values are sequentially calculated with the N focal plane images collected in the step 2, and the calculated RMS values are averaged to be used as reference RMS values;
and 4, calculating according to the wavefront detection precision of the coronagraph and the effective stroke of the deformable mirror to obtain a second control signal of the deformable mirror, adding the second control signal and the first control signal of the reference wavefront, sending the second control signal to the deformable mirror through the coronagraph control system, and shooting a focal plane image of the system.
Assuming that the wavefront detection precision of the coronagraph is designed to be lambda/1000 (lambda is the working wavelength), the effective stroke of the deformable mirror is 1.5 μm, and the corresponding control signal range is 0-1. Then the control signal of the deformable mirror corresponding to the wavefront detection accuracy of lambda/1000 can be calculated to be lambda/1500. This value is added to the control signal of the reference wavefront and sent to the deformable mirror by the coronagraph control system and the system focal plane image is taken.
where m and n are the number of dark field image rows and columns, xmnIs the pixel value, x 'of the image shot in step 3 at the (m, n) position'mnThe pixel value of the image at the (m, n) point is taken for step 2 or step 4.
And 4, calculating the RMS value between the reference image and the image in the step 4, and when the calculated RMS value is larger than the reference value, proving that the wavefront detection precision of the designed coronagraph meets the requirement of a design index.
In summary, the invention provides a method for detecting and calibrating the wavefront of a coronagraph with ultrahigh precision, which comprises the following specific steps of 1, constructing a set of coronagraph system with a deformable mirror as a core; step 2, controlling a coronagraph control system to send a first control signal to a deformable mirror to enable the deformable mirror to generate a high-contrast dark area on a focal plane, and shooting a focal plane image at the moment as a reference image; step 3, according to the wavefront detection precision design index of the coronagraph, applying a second control signal to the deformable mirror; and 4, judging whether the wavefront detection precision of the system meets the design requirement or not by evaluating the difference between the reference wave surface and the wave surface in the step 3. According to the wavefront detection method, extra detection components are not needed, and only the deformable mirror in the coronagraph system is used, and a control signal is applied to the deformable mirror through the deformable mirror, so that the ultra-high-precision wavefront detection and calibration can be realized through evaluating the dark image of the focal plane.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. The method for detecting and calibrating the wavefront of the coronagraph with high precision in high contrast imaging is characterized in that the contrast ratio is better than 10-6The wavefront detection and calibration precision of the coronagraph is in the range of 1/100-1/10000 working wavelength, and the specific steps are as follows:
step 1, building a set of optical system of the coronagraph with a deformable mirror as a core; wherein the anamorphic lens is placed at a pupil of the system and is conjugate to the primary mirror of the telescope;
step 2, the coronagraph control system sends a first control signal to the deformable mirror, a high-contrast dark area is generated on a focal plane, and N focal plane images are shot by using a focal plane camera;
step 3, averaging the N images collected in the step 2 to obtain a reference image, sequentially calculating RMS values of the reference image and the N focal plane images collected in the step 2, and averaging the calculated RMS values to obtain a reference RMS value;
step 4, calculating according to the wavefront detection precision of the coronagraph and the effective stroke of the deformable mirror to obtain a second control signal of the deformable mirror, adding the second control signal and the first control signal, sending the second control signal to the deformable mirror through the coronagraph control system, and shooting a focal plane image of the system;
step 5, evaluating the wavefront detection precision of the system by evaluating speckle changes in dark areas on the focal plane image and the reference image; and 4, calculating the RMS value between the reference image and the focal plane image in the step 4, wherein when the RMS value is larger than the reference RMS value, the wavefront detection and calibration accuracy of the coronaries system reaches the requirement.
2. The method for detecting and calibrating the ultrahigh-precision wavefront of the high-contrast imaging coronagraph according to claim 1, wherein in the step 3 and the step 4, the following evaluation functions are adopted in the evaluation process:
where m and n are the number of rows and columns of the image, xmnIs the pixel value, x 'of the image obtained in the step 3 at the position of (m, n)'mnThe pixel value of the image shot in step 4 or step 1 at the (m, n) point.
3. The method for ultrahigh precision wavefront measurement and calibration of high contrast imaging coronaries according to claim 1, wherein said wavefront measurement and calibration method uses only deformable mirrors and focal plane cameras within the coronaries without additional devices.
4. The ultrahigh-precision wavefront measuring and calibrating method for high-contrast imaging coronaries according to claim 1, wherein the relative wavefront precision is measured, that is, the change of the wave surface generated in step 3 relative to the wave surface generated in step 2 is measured instead of the absolute wavefront precision.
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| CN113639864A (en) * | 2021-08-16 | 2021-11-12 | 中国科学院国家天文台南京天文光学技术研究所 | Space full-area ultrahigh contrast imaging method and coronagraph system |
| CN114137721A (en) * | 2021-10-15 | 2022-03-04 | 中国科学院国家天文台南京天文光学技术研究所 | High-contrast imaging coronagraph micro-point density modulation system and working method |
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| CN103399401A (en) * | 2013-07-15 | 2013-11-20 | 北京理工大学 | Wavefront error correction system and method for inhibiting speckle noises of coronagraph system |
| CN111413806A (en) * | 2020-04-08 | 2020-07-14 | 中国科学院国家天文台南京天文光学技术研究所 | Dual-mode switching system for space coronagraph and switching method thereof |
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Cited By (3)
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| CN113639864A (en) * | 2021-08-16 | 2021-11-12 | 中国科学院国家天文台南京天文光学技术研究所 | Space full-area ultrahigh contrast imaging method and coronagraph system |
| CN113639864B (en) * | 2021-08-16 | 2023-06-23 | 中国科学院国家天文台南京天文光学技术研究所 | Space full-area ultrahigh contrast imaging method and star crown instrument system |
| CN114137721A (en) * | 2021-10-15 | 2022-03-04 | 中国科学院国家天文台南京天文光学技术研究所 | High-contrast imaging coronagraph micro-point density modulation system and working method |
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